Seismic surveying



Feb. 19, 1952 J. O. PARR, JR

SEISMIC SURVEYING Filed Jan. 12, 1949 (Jam, 6% 8mm? a/Jm ATTORNEYSPatented Feb. 19, 1952 SEISMIC SURVEYING Josephus Overton Parr, J12,Sa'n- Antonio,-' Tex,- assignorto Olives. Petty, San Antonio, Tex.

Application J anuary 12, 1949, Serial No. 70,402

(Cl. 18I".5)

9 Claims;

This invention relates an improved method of. propa ating seismic waves..in..underwater. formations and-to, apparatussuitable. for. use in .the

practice of. the method More.,particularly.,. itJS. an object, oitheinvention-to. provide .an improved method. and apparatus .for detonatinga charge.

of explosive in water .in.. geophysical prospecting.

of underwater .stratabymeans of whicha num:. ber ofdifiicultiescommonly. encountered in pres.- ent practice. .canbeminimized or av.oided,-and which will. permit the detonationof.,explosi.ves at depths. greater, than those. nowcommonly. regarded.as the-optimum, with resultant. increase in the efliciency of theexplosive.

It. is; well known thatgthe. damage,.to..marinelife. resultingirom. .thefiring. of explosives under watermis .caused principally. bytransmission.

throughthe water, of.,high velocity energy waves of supersonic.frequency, whereas useful seismic wave, energy,-,withinpthe sound,range,.,is..not in: H

jurious to most living organisms". I have his? covered-that themagnitude of. supersonic. energy released by an explosion beneath watermayi be-i greatly reduced if the explosive chargeis oetonated in agaseous-medium by which the charge, is isolated from direct contactwiththewatendor instance eby the provision of- -a gaseous ,pocket inn-whichthe ,charge' is suspended andswithin Pre-. i sumably the-explosiveshockis cushioned by 1 the.

which the:- initial expansion'can occur;

gaseous medium and-the initial impact correspondingly reduced. Whateverthe cause; it can.

be. shown that. a charge .so exploded dissipatesmuch-less energy in theform of waves havinga' velocity of the order of 5,000 feet' or more per:

second, and" causes -no substantial damageto-v marine life.

I ;have alsofound. that :when. a charge is detonated under, water-;;andin a surrounding gaseous pocket, the bubble ,efiectnoted by-Layet;al.,in U. S. Patent 2,351,524, granted'June .13, 19.44,--.is1practically eliminated. even though the.- charge: is exploded at such ,adepth that; blow-- out? of the. Wateriabove the explosioncannot'ocr;Consequently I am' enabled by the practice cur. of the present inventionto improve theeificiency of the explosive in generating seismic:wavesrin theunderlying strata without giving'rise, toisec ondary Pwaves of undesirable magnitude.

In the preferred method of practicing the invention, the gaseous pocketmay be provided by suspending the explosive charge within an enclosure,for instance a balloon or a bell, which is positioned at the desireddepth in the water in any conventional manner beforefiring." Al-yternatively, a .gaseous pocket mayv be created around the explosive byfirst detonating a relatively small gas releasing charge, whereby thegaseous "pocket isformed in -situ immediately before the firing of thecharge which propagates the seismic waves:

Further objectsandjeatures' of the inventionwill'flbe apparent from thefollowing description taken in. connection. with" the accompanyingdrawings, in whichf.

Figure 1 illustrates :one form of equipment satisfactory for thepractice of the invention, in which the. gaseous medium is confinedwithin an enclosure;

Figure 2*? illustrates: an alternative method wherein the surroundinggas pocket is formed by the detonation of. a gas-producing charge priorto thefiring of. the main explosive; and

Figure Srepresents. a modification of Figure 1 in which ,thehcharge.is'. suspended in the air trapped within .a bell havinganopen bottom.

In order. to facilitate. an understanding of the invention, referenceis, .I'nade herein. to specific methods and. apnaratflsbu't it will ,beunderstood thatno limitation of the. scope of, the invention is thereby.intended, variousiurthen methods and alterations, such as .wouldoccur.to those skilled in the art, being ,contempla'ted herein.

Referring fir'sttoi Figure .1, it. .will'jbe observed that-thev chargeofiexplosive I0 is suspended in an enclosure. constituted .by 13-balloonl I, the. supporting, line. ;.I 2 .ttherefor being secured to theupper 'sideottheballoonat l3.' Aweight 18 may be secured totheiballoonfor.instance by snood lflorzthelikeuto carry. thelballoondown, a line E5of'selected'length:servingrto position the balloon at thedesireddepthwhen theweight l8 rests on the. bottom. The. balloon maybefilled with air or any: othersuitable gaseous medium,v the. latter term'beingiemployedherein to include air. Suitable; electricalconnections,.such .as the usual shot line...20,.may extend throughlinel2 to a detonating cap or the like associated with .the explosive chargeI, 0, .Itwillbe applfciated thatthe. balloon andichargetmay be.suspendedfrom the. surface of the,-watertin;thgconventionalrmanner .by a

the high ,velocity .-waves..commonly dissipated.

thmugnwnee-ty the-.firingiof an.explosive thereinsane: suppressed.sutficiently to.e1imina.te damagetofishrandothenliving,organismsanddisturbing effects-iofesecondai'fy,-P..waves. ar e minimized, so that thetformula prescribe'd in" thepatent. to Lay et algfabove mentioned need not be observed.

In Figure 2 is shown a modification whereby the gaseous pocket iscreatedxiimmediately' prior to; the detonationof'the main charge: Thismay be achieved by positio'ning the charge-l0 within a sleeve'or.container22, which may be formed or wood or {water-resistant; fibrousmaterial. A gas releasing charge; for'instance a detonating fuse 23offthe type known as fprimacord, is wrapped around the sleeve 22;the-latter serving to space the. illsefronithe main'charge. I 0. l Oneend of the fuse extend's'into' the main charge [0 at to detlength, andthe cap 25 is detonated by a shotline 29 or other electricalconnections.

It will be appreciated that on detonation, the

fuse 23 first evolves a gas which forms a gaseous explosive ispositioned-above the level of water rising in the bell as the latter islowered. The bell is carried on a line 35 depending from a float 37, thelength of line 36 being such that the, de-

sired depth is reached. Detonation is effected by I a shot line 20,which may be carried down .to the charge i0 throughline 36. In order..to ensure that the bell will remain in the proper. position whenlowered, a weight 38 may be secured byv lines 39 to the open mouththereof. 7

The bell 35 may be fairly heavy, for instance being formed of metal, andmay have .a substantially parabolic shape, so that when the char e ispositioned substantially at the parabolic focus, the energy released bythe explosion will be refiected downwardly .in parallel or convergingwaves, whereby the force of :the explosion is concentrated and theefliciency of the explosive cor-U respondingly increased. The effect maybe heightened by the use of a baflle plate 40, which may be circular inplan, suspended within the bell on support rods 4|, and positioned.beneath.

the charge to reflect against the inner surface of the bell the energyof the explosive. By means of this structure I am enabled to propagateseismic waves of adequate magnitude Withi a charge of substantially lesssize.

It will be perceived from the .foregoing that the basic concept of theinvention is the generation of an explosion within a pocket ofgas andbeneath the surface of the water; Various types of equipment, capable ofachieving this end, may be substituted for that illustrated herein.

Having thus described the invention, what is claimed as new and desiredto besecured by Letters Patent is: v 1. In apparatus for propagatingseismic waves in underwater formations, the'combination with theexplosive charge, of a casing containing a gaseous medium throughwhichthe major p9 tion of the energy released on detonation of thecharge is transmitted directly to the water, means suspending saidcharge in said casing and in (l0 charge, said casing having a volume.many'times that of the explosive charge, and sufiicient to said medium,and means; for detonating said materially reduce the "transmissionthrough the water of wave energy having velocities in excess of 5,000feet per second, thereby minimizing damage to marine life.

2. In apparatus for propagating seismic gaseous medium, means suspendingsaid charge in said casing and in said medium, and means for detonatingsaid charge, said casing compris-.

ing a bell having an open bottom whereby. the I energy released by theexplosion is reflected downwardly, said casing having a volume manywaves. in underwater formations, the combination with the explosivecharge, of a casing containing a,

times that of the explosive charge, and sufiicient to materially reducethe transmission through the water of wave energy having velocities inexcess of 5,000 feet per second, thereby minimizing damage to marinelife.

3. In apparatus for propagating seismic waves I V in underwaterformations, the combination with the explosive charge, of a casingcontaining a gaseous medium, means suspending said charge in said casingand in said medium, and means for detonating said charge, said casingcomprising a bell having an open bottom whereby the energy released bythe explosion is reflected downwardly, and baffle means within said belland below said explosive charge to impede downward dissipation ofunreflected energy.

4. In apparatus for propagating seismic waves in underwater formations,the combination with the explosive charge, of a gas releasing chargedisposed in proximity to said explosive charge for forming when igniteda gaseous pocket around the latter, and means effecting in quicksuccession ignition of said gas releasing charge and detonation of saidexplosive charge.

5. In apparatus for propagating seismic waves in underwater formations,the combination with the explosive charge, of a gas releasing chargedisposed in proximity to said explosive charge for forming when igniteda gaseous pocket around the latter, said gas releasing charge comprising.a ,detonating fuse of substantial length extending about said explosivecharge and having one end thereof in firing relation with the latter,and means effecting detonation of the other end of said fuse, whereby agaseous pocket is formed, by the burning of said fuse, around saidexplosive charge immediately prior to detonation thereof.

6. A method of propagating eismic waves in underwater formations whichincludes the step of detonating an explosive charge at a point beneaththe surface of the water and substantially above the bottom, and withina gaseous pocket having a volume many times that of the explosivecharge, and sufficient to materially reduce the transmission through thewater of wave energy having velocities in excess of 5,000 feet persecond, thereby minimizing damage to marine life, the major portion ofthe energy released by detonation of the charge being transmittedthrough the gas in the pocket directly to the water.

7. The method recited in claim 6 in which the gas constituting thegaseous pocket is confined in a gas containing envelope.

8. The method recited in claim 6 in which the gas constituting thegaseous pocket is formed by the step of firing, immediately prior to thedetonation of the explosive charge, a gas evolving charge in proximityto the main charge.

9. The method recited in claim 6, which includes the further step ofreflecting downwardly and in a confined path the major part of theenergy released by detonation of the charge.

JOSEPHUS OVERTON FARR, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

